Insects like weather – you never know what to expect

Mid-South insect infestations this spring have featured many of the usual suspects, thrips, bollworms, plant bugs and spider mites. But unexpected visitors are also crashing the party, including surprisingly high numbers of yellow-striped army worms.
Spider mites and plant bugs have been heavy in Arkansas, Mississippi and Tennessee.
Cotton bollworm trap counts in Arkansas are 20 percent to 30 percent higher than last year, which was a heavy bollworm year.

In the Mid-South, insects are a lot like the weather. From year to year, you never know what to expect. So far this season, insect infestations have featured many of the usual suspects — thrips, bollworms, plant bugs and spider mites. But unexpected visitors are also crashing the party, including surprisingly high numbers of yellow-striped armyworms, according to state entomologists.

Arkansas

“The hot, dry weather has been very conducive to a lot of our pests, and right now, we’re experiencing a huge yellow-striped armyworm outbreak in soybeans,” said Gus Lorenz, Extension entomologist, University of Arkansas. “There are a lot of applications going out, and it is causing some severe defoliation in a lot of cases.”

The problem is statewide, according to Lorenz, “from Clay County all the way down into southeast Arkansas.”

In cotton “plant bugs are really rolling as our cotton nears bloom. We’re seeing a lot of pre-bloom, treatment-level plant bugs that in a lot of cases are three to four times the threshold.”

Lorenz said spider mites are a problem “from one end of the state to the other, where it’s been dry.”

Lorenz said cotton bollworm trap counts, which have been monitored since the beginning of May “have yet to peak on population. The numbers continue to keep going up. Our trap counts are 20 percent to 30 percent higher than last year, which was a heavy bollworm year. Right now, we’re seeing a big egg lay of bollworms, particularly in the south part of the state, but it’s creeping north.”

In rice, “chinch bugs have been the worst I believe I’ve ever seen,” Lorenz said. “We’ve sprayed more acres in rice than I’ve ever seen. We’ve also had false chinch bugs in cotton and soybeans. It’s been a busy insect year so far, and it’s not shaping up for a quiet rest of the summer.”

Mississippi

According to Angus Catchot, Mississippi State University associate Extension professor of entomology and plant pathology, spider mites and plant bugs have been primary pests in cotton. “Up until recently, we’ve under some serious drought stress, which has exacerbated the problems we’ve been having with spider mites. We’ve been treating a number of acres, particularly in the south Delta.”

Plant bug numbers “have been very high,” Catchot said. “We’ve been dealing with a lot of migration out of corn, Group 4 soybeans and other wild hosts. It’s required a number of treatments to keep them under control.”

Catchot is concerned that the lateness of the cotton crop — much of which had not reached the flowering stage by the end of June — could be problematic at the end of the season. “We have data that shows that early planting can reduce insecticide sprays on plant bugs by 50 percent to 60 percent.

“Well beyond 50 percent of the crop was planted past May 10 to May 15. We’re dealing with big migrations of adult plant bugs into the fields. Producers make an application, and when they check the field again, the numbers are the same or even higher. It’s not that they’re not getting control. The bugs are just moving in behind them. We’re hoping that this will start to slow down in the next 10 days to two weeks.”

In the north Delta, Palmer pigweed “is a tremendous host for tarnished plant bugs. That is going to be a constant source of plant bugs.”

Catchot says growers “have to stay on top of populations that are moving in. When square retention starts dropping, we’re going to have to tighten our intervals. We may not be able to get seven to 10 days out of the products available to us.”

Insects in soybeans as of the end of June “have been abnormally quiet to this point,” Catchot said.

Tennessee

Tennessee Extension entomologist Scott Stewart says many cotton producers were still battling thrips toward the end of June, and plant bugs pressure is heavy.

“Replanted cotton is struggling. We have some cotton at three-leaf, and we have cotton just beginning to flower. The general scenario is that once we get to nine or 10 nodes, we have enough plant bugs to treat. A lot of times, a week later, we have enough plant bugs to treat again. It’s just been a continuing migration, and the rains we’ve received have not been helping. Producers are getting sprays on, and they get a rain on shortly afterwards, which is knocking off some of our residual control.”

Stewart says the plant bug infestation was not all that unusual. “When we have a cold winter and a wet spring, we build up a lot of plant bugs on wild hosts. When we had those two weeks of hot weather, it pushed all those hosts to mature quickly, which coincided with a lot of our early cotton starting to square.”

However, Stewart didn’t expect numbers to build to the highest levels he’s seen during his tenure in west Tennessee. “We’re not the Mississippi delta. It’s not uncommon for us to get to first bloom needing only one spray for plant bugs. But this year, we’re going to average between two and three applications prior to bloom.”

Louisiana

Jack Baldwin, Extension entomologist, LSU AgCenter, says insect pressure in corn, grain sorghum and soybeans “has been light and scattered so far. The corn crop is finishing up, but I haven’t received a lot of reports of corn borer or stink bug activity. In grain sorghum, we’ve had a few reports of sorghum midge.”

Baldwin says the insect pressure in the state’s soybean crop “has been pretty light. Stink bugs haven’t been too bad, and I haven’t heard very much about the redbanded stink bug. But as we get into July and later into the summer, foliage feeding worms are more likely to be a problem.”

Missouri Bootheel

Kelly Tindall, an entomologist at the University of Missouri Delta Research Center, says populations of Japanese beetles are building up in ditch banks and turnrows in southeast Missouri. “We’re also catching a lot of corn earworms in our traps, and we have some reports of fall armyworms in whorl stage corn, which is early for us.”

Producers have reported stink bug building up in roadside weeds, according to Tindall. “Aphids are starting to pop up in cotton. We’re also hearing about problems with herbicide carryover, which adds another stress on plants.”